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Drcool
Drcool, HVAC Technician
Category: HVAC
Satisfied Customers: 2077
Experience:  i have been an A/C tech for the past 12 Years. working on window types, split type, and package
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Central Air conversion from R22 to R407C is not cooling enough... I

Resolved Question:

Central Air conversion from R22 to R407C is not cooling enough...

I had R22 central air system which worked adequatly. The evaporator produced temperature in the range 35-40 degrees.

The compressor got flooded during Sandy, and was replaced with the new R407C based unit. No changes were made to evaporator. The low side pressure is around 60 psi, the high side pressure is around 180 psi. The evaporator is barely cold - 50 degrees or slightly higher. I tried evacuating refrigerant to reduce low side pressure in hopes to achieve lower temperatures in evaporator. I was gradually dropping the pressure to 55-50-45-40. The reduction of evaporator temperature was very small, and eventually it started freezing a little bit, at which point I had to stop.

Please advise what is wrong and what needs to be done.
Submitted: 1 year ago.
Category: HVAC
Expert:  Drcool replied 1 year ago.

Drcool :

Hello, Is the metering device an expansion valve or an orifice type fixed capillary? If it is an expansion valve, have you tried adjusting the superheat?

Customer:

I am not sure. How do I check? I've heard the contractor mentioning the term orifice.

Customer:

I am pretty handy, so whatever I can do I don't mind doing...

Drcool :

Hello, If the metering device is a fixed orifice, then it is not adjustable. You can not do anything to adjust the super heat of the unit.

Drcool :

Can you enlighten me please. You mention of a contractor, I am thinking you are the contractor. SO, if you are the customer, and you are not satisfied, can you not contact your contractor and tell him you still have issues with the conversion?

Drcool :

If you are the customer, then adjusting the super heat would be expensive since you would need hvac tools to do that. It should be done by an HVAC engineer.

Customer:

Hello, I opened up the cover of the evaporator, it's definitely an orifice and a bunch of small tubes leading to the main evaporator. I am a customer, not a contractor. Why would you think I am a contractor?

Drcool :

Because of the many questions that you have placed here on the site. Some contractors are doing it here. Anyway, So, it is an orifice so we can not adjust the super heat.

Customer:

Anyway, I was adding more refrigerant little by little while observing the temperature and freezing of the evaporator. As I reached 48 psi (190 psi on high side), the evaporator stopped freezing, and most of it maintained pretty cool temperature around 40 degrees. So, based on my experience with this unit, the optimal temparature is 48 degrees. Above that, the avaporator produces little cold, while below that it starts freezing. Based on this information, would replacing an orifice with larger or smaller flow orifice be beneficial?

Drcool :

I would say, stop on the 48 psi where the temp of the inlet tubes are coldest. Would you know the temperature of the outlet tubes of the evaporator coil?

Customer:

Yes, I measured all of them, and the range is 35-45 degrees. The further from the capillars, the higher the temperature, and vice versa. I have another small practical question. While I am disconnecting the high pressure hose, a lot of the refrigerant escapes by the time I completely unscrew the cap and the valve closes. What is the right technique?

Drcool :

Was there a valve on the high pressure side? Or it is just a shreader valve like the one on tires?

Customer:

Just like on tires, and just like on the low pressure side.

Drcool :

Ok. What I can suggest is to turn the unit off , let the pressure stabilize, then hold the hose downward towards the pipe while loosening the round fitting of the hose. If you know that the whole fitting is unscrewed, let go of the hose and remove it. A small amount of liquid would come out but not sticking the valve open and letting a lot of liquid refrigerant flow out. I suggest use gloves to prevent frost bite.

Drcool :

By the way, did the contractor flush the system from its old oil?

Drcool :

When I say the outlet tubes of the evaporator, I mean the tubes that comes out of the evaporator going to the compressor. That would be the big pipe as all of the other pipes connects together and comes out as one. That would be the pipe to measure the temperature. Then we can compute the super heat.

Drcool :

Also, when you are adding refrigerant, use the liquid from the tank to add the refrigerant. R-407 gas has different blends form its liquid form and liquid is needed to charge a system.

Drcool :

Hello....are you still here?....

Drcool :

Hello, I am sorry but I have to leave. I will check again later and see if you have responded. With your question if you need a bigger orifice or a smaller, we need to find out what is the temperature of the outlet pipe first in order to find out what is the super heat so we can decide if we need a bigger orifice. Thanks

Customer:

Hello again, sorry I didn't realize you responded...

Customer:

Thank you for the recommendation on disconnecting the high pressure hose. That's what I was thinking. And yes, at least I figured to use gloves. They were all frozen.

Customer:

When I was charging, I was moving the can around to make sure the content is mixing. But I kept it vertical, so I am pretty sure it was gas and not liquid entering the system. Now I recal the contractor putting the can on its side, and now I understand why.

Customer:

I think the contractor flusshed the system. He was using some sort of compressor connected to it. I wasn't watching all the time.

Customer:

The temperature of the retrun tube at the compressor was around 50-55 degrees, but I am not sure. Would need to measure later on...

Expert:  gotoman for ac replied 1 year ago.
Russ here.. Trane Service Manager. Let me jump in herere. accept will go to other tech. If you google R 407a you will see it is not recomended for air conditioning applications only refrigeration. You loose efficiency. 421A is the one I recomend . You it on numerous occasions with no problems and no lose of efficiency. Russ
Customer: replied 1 year ago.


Russ, thank you. Type of refrigerant was not my choice.

Expert:  gotoman for ac replied 1 year ago.
Your welcome. Just sounds like a bad installation. Russ
Expert:  Drcool replied 1 year ago.
Hello ,

I agree with Russ, if R407 was used, you would loose efficiency since it would need a bigger evaporator to equal the cooling efficiency of R-22.

But, if you have R-407 now on the system, then you can just try to adjust what you can so that at least you can make it work as cold as the R-22 before.

So we start from the beginning. If you can recover the refrigerant, evacuate the system, replace the orifice with the next bigger opening, and slowly charge it with liquid refrigerant until the frost on the outlet of the orifice melts.

Then measure the outlet temperature of the evaporator and we would see what would be the super heat.

Or, if you can still change refrigerant, then might as well use R-421A as Russ suggested.

-
Customer: replied 1 year ago.


Thanks for your suggestions. Over the weekend, I found the sweet spot which corresponds to 48 psi. I followed the same logic you mentioned - gradually adding refrigerant to the point the orifice and capillars stop freezing. It's been cooling for two days now, and with good results. In order to replace orifice, I would neet to call the contractor who will charge me for all the work and for an additional refrigerant to recharge the system. I will see if I can get away with how it performs now. Thanks again.

Expert:  Drcool replied 1 year ago.
Hello,

That is nice to hear.

I just hope it would already work that way so you would no longer spend some more on the repair.

Thank you for using this service.

-
Drcool, HVAC Technician
Category: HVAC
Satisfied Customers: 2077
Experience: i have been an A/C tech for the past 12 Years. working on window types, split type, and package
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